The industrial preparation of alkylene oxides and alkylene glycols is generally known.
Alkylene oxides are usually obtained industrially by oxidation of alkenes. In the known industrially relevant processes, the corresponding alkylene glycols are formed as by-products by reaction with water present in the reaction system according to the exothermic reaction:alkylene oxide+H2Oalkylene glycol  (1).
In addition, subsequent reactions to form higher alkylene glycols such as dialkylene and trialkylene glycols take place according to the formulae:alkylene oxide+alkylene glycoldialkylene glycol  (2), andalkylene oxide+dialkylene glycoltrialkylene glycol  (3).
In general, alkylene glycol concentrations of up to 10% are obtained here. These alkylene glycols are usually removed as high boilers together with the water from the alkylene oxide plant. Before release into the environment, this process water has to be purified, typically in a biological purification plant. The alkylene glycols present in this process water result in a very high COD value or a very high burden of biodegradable substances, so that the biological purification plant has to be made very large and the water generally has to be diluted beforehand. In addition, alkylene glycols are materials of value. As an alternative to an enlarged biological plant, the alkylene glycols can be removed by distillation, but this requires a high outlay in terms of energy and apparatus.
Alkylene glycols are obtained industrially by reaction of pure alkylene oxides in an aqueous phase corresponding to formulae (1), (2) and (3). The reactions according to (1), (2) and (3) take place at a considerable excess of water of, for example, about 10-20 times the stoichiometric amount. This water is generally removed from the reaction system in a first step by multistage vaporization and is, after condensation, fed back into the reactor. The alkylene glycol mixture formed is then separated into the individual glycols in a series of rectification columns. Due to the large amounts of water to be vaporized, large quantities of energy have to be introduced.
According to the invention, a conventional and known alkylene oxide plant and a conventional and known alkylene glycol plant are modified and combined with one another in such a way that                both alkylene oxide and alkylene glycols or alternatively alkylene glycol ethers can be produced,        the alkylene glycols and alkylene glycol ethers formed in the alkylene oxide plant are recovered as materials of value and the load on the downstream purification plant is thus also reduced,        energy integration can take place,        no fresh water has to be introduced and        unpurified or only partially purified alkylene oxide can be used.        
In addition, the preparation of alkylene oxides is frequently carried out in methanol as solvent. This has to be recovered after the reaction in order to be able to be recirculated to the process. Such a work-up process is described in DE 102 33 388 A1 (corresponding to WO 2004/009566 A1). Further processes for preparing alkylene oxides use other organic solvents. WO 2009/001948 A1 describes the reaction of propylene, hydrogen and oxygen to form propylene oxide in acetonitrile or in aqueous acetonitrile.
In conventional processes for preparing alkylene oxides, the starting material alkene is reacted in the liquid phase with an oxidant. The reaction can be carried out with addition of a catalyst. Oxidants which have been found to be useful are chlorine, hydroperoxides and preferably peroxides, particularly preferably hydrogen peroxide. The reaction takes place in a reactor, typically in a shell-and-tube reactor. In this, the alkene reacts with the oxidant to form alkylene oxide, possibly with formation of intermediates such as chlorohydrins which are subsequently converted into the alkylene oxide. Apart from the desired product alkylene oxide, alkylene glycols are formed to a small extent in the reaction. These compounds are, on the one hand, valuable chemicals but owing to the small amount can generally only be isolated with a high outlay in terms of apparatus and a high energy consumption, so that they have hitherto had to be disposed of in the work-up of the reaction residues. DE 102 33 382 A1 describes a process for the continuously operated pure distillation of the 1,2-propylene glycol obtained in the coproduct-free synthesis of propylene oxide. U.S. Pat. No. 7,332,634 B2 describes a continuous process for separating off 1,2-propylene glycol which is obtained as by-product in the preparation of propylene oxide.
The reactor for the preparation of the alkylene oxide is followed by separation of the reaction mixture into product, unreacted starting materials, water and any organic solvents present, typically in rectification columns. Low-boiling by-products preferably leave the plant with the flushing gas while high-boiling by-products preferably leave the plant with the water used for dilution of the reactants or with the water formed in the reaction. This wastewater generally has to be diluted further before introduction into a biological wastewater treatment. An alternative approach separates organic compounds from the undiluted wastewater by distillation, so that less polluted wastewater is passed to the subsequent treatment stage. However, this requires a high consumption of energy.
Examples of the preparation of alkylene glycols from alkylene oxides may be found in WO 2004/085375 A1, EP 0 226 799 B1, U.S. Pat. No. 3,574,772, U.S. Pat. No. 4,937,393, DE 29 38 115 C2 and DE 197 26 508 A1. It is also possible to produce alkylene glycols from alkenes by direct reaction. Examples of this may be found in U.S. Pat. No. 4,203,926 and in U.S. Pat. No. 4,308,409.
In a conventional process for preparing alkylene glycols, the starting material alkylene oxide is mixed with water and passed through a reactor, typically a simple adiabatic tube reactor. In this, the alkylene oxide reacts with water in an exothermic reaction to form alkylene glycol. Apart from the simple alkylene glycol, higher alkylene glycols, i.e. mainly dialkylene glycol and trialkylene glycol and possibly also very small proportions of yet higher alkylene glycols, are generally formed. These compounds are likewise valuable chemicals. Typical ratios of alkylene glycol to dialkylene and trialkylene glycol are about 100:10:1. The reaction can be carried out with addition of a catalyst. The process employs large amounts of water which are generally circulated. These are necessary in order to remove the heat of reaction and to suppress the formation of higher alkylene glycols by diluting the alkylene oxide and the alkylene glycol.
After the reaction mixture has left the reactor, the water is firstly separated off, for example in a rectification column or in a simple evaporation. To save energy, a plurality of evaporators or rectification columns are frequently connected to one another.
The removal of water is followed by separation into the various alkylene glycols. This is generally carried out in rectification columns. Here, the alkylene glycol, the dialkylene glycol and finally the trialkylene glycol are separated off in order, in each case at the top or at the side offtake stream. High boilers present are taken off in the bottoms from the trialkylene glycol column and are generally discarded, for example by incineration. In some process variants, this third column is omitted because of the small amount of trialkylene glycol formed and the bottoms from the dialkylene glycol column are discharged from the plant and discarded. This process and this process variant are generally known.
Plants for the preparation of alkylene oxides and for the preparation of alkylene glycols have hitherto been operated separately although at present about 20% of the alkylene oxide produced is used for the preparation of alkylene glycols.
However, it has already been proposed that alkylene glycols and alkylene oxide be prepared in one plant and these products subsequently be separated from one another. An example of this may be found in WO 02/088102 A1. However, nonliquid and nonaqueous systems are used here and the reactions take place in the gas phase. The process has not been implemented industrially to the present time.
Combinations of plants in which various substances are reacted with one another and separated are already known. DE 10 2004 054 047 A1 describes a process for preparing 1,6-hexanediol from a carboxylic acid mixture comprising adipic acid, 6-hydroxycarboxylic acid and 1,4-cyclohexanediols by esterification of the carboxylic acid mixture, removal of the 1,4-cyclohexanediols by distillation, hydrogenation of the purified ester fraction and isolation of the 1,6-hexanediol by distillation. DE 10 2008 007 081 A1 describes a process for preparing n-butene oligomers and 1-butene from industrial mixtures of C4-hydrocarbons. Here, a starting material is firstly purified and worked up by distillation. A high boiler fraction obtained is subsequently reacted catalytically, resulting in the n-butenes present being oligomerized. DE 10 2005 006 974 A1 describes a continuous process for preparing cyclohexyl(meth)acrylate. Here, cyclohexanol is esterified with pure (meth)acrylic acid, neutralized, washed and subsequently purified by multistage distillation. In these processes and plants, neither alkylene oxide nor alkylene glycols are produced.
The coupling of a plant for preparing alkylene oxide with a plant for preparing alkylene glycol has also already been proposed. An example of this may be found in DE 102 33 385 A1 (which corresponds to WO 2004/009568 A1). Here, the alkylene glycol formed in the two plant sections is discharged from the respective plant section and combined in the work-up of the alkylene glycols. In addition, fresh water is fed into the reactor for preparing alkylene glycol. The process described in these documents comprises coupling of the production of propylene oxide with the production of propylene glycols. However, the crude propylene oxide originating from the propylene oxide plant is reacted in the second reactor with water which does not originate from the first reactor. In addition, the propylene glycol mixtures obtained in the stages of propylene oxide production and propylene glycol production in the previously known process are combined and the individual propylene glycols are then separated off by distillation. Thus, in the previously known process, the reaction mixture which originates from the first reactor and has been freed of propylene and if appropriate of propylene oxide is conveyed past the second reactor and later combined with the propylene glycol mixture originating from the second reactor. This reaction mixture from the first reactor contains a considerable amount of water which essentially has to be removed either before or after this reaction mixture is combined with the propylene glycol mixture originating from the second reactor. Thus, the previously known process requires separate removal of the water from the first reactor and of the water from the second reactor, which results in a considerable outlay in terms of energy and capital costs since energy-intensive circulation of the water has to be carried out.
There is a continuing search for processes and measures by means of which the efficiency of these processes can be improved and by means of which these basic chemicals can be prepared more economically.